FIG. 1 illustrates the architecture of a conventional cellular communication network, for example the Personal Digital Cellular system. The mobile station or mobile subscriber unit MS is capable of conducting both circuit-switched communication and packet-switched communication in the cellular network. Moreover, the cellular network supports voice communication via circuit-switched connections and via packet switching. The mobile subscriber unit typically has a permanent address, for example an Internet Protocol (IP) address which is known by the network. The data terminal equipment (DTE) attached to the mobile subscriber unit is configured with the IP address.
When the Gateway Packet Mobile Services Switching Center (GPMSC) receives an incoming IP voice packet from the Internet Host IH via the Internet, GPMSC checks with the home location register HLR and the Visited Mobile Services Switching Center VMSC to see if the mobile subscriber unit MS to which the IP voice packet is directed is already busy in a circuit-switched (CS) call. The HLR tells GPMSC whether or not the mobile subscriber unit is in the packet mode, and the VMSC tells the GPMSC whether the mobile subscriber unit is in CS mode or is idle. If it is determined that the mobile subscriber unit is already busy in a CS call, then the incoming IP voice packets directed to the mobile subscriber unit will be rejected. If, on the other hand, the mobile subscriber unit is not busy in a circuit-switched call, then the GPMSC sets up a packet channel to MS/DTE, and an IP voice session between the Internet Host IH and the mobile subscriber unit can be established.
Also shown in FIG. 1 are a Visited Packet Mobile Services Switching Center VPMSC, a Gateway Mobile Services Switching Center GMSC, a Public Switched Telephone Network PSTN, an Integrated Services Digital Network ISDN, and a radio network, all well known components of a conventional cellular network architecture.
The above-described conventional operation of the GPMSC is illustrated in FIG. 2. If an IP voice call is received at 21, it is determined at 23 whether or not the mobile station is busy in a circuit-switched call. If the mobile station is busy in a circuit-switched call, then the IP voice packets are rejected at 25. If the mobile station is not busy in a circuit-switched call at 23, then the GPMSC sets up a packet channel to MS/DTE, and an IP voice session between the Internet Host IH and the mobile subscriber unit can be established at 27.
It is desirable in view of the foregoing to process incoming packet-switched voice calls such that the voice packets are not rejected if the mobile subscriber unit to which they are directed is busy in a circuit-switched call.
According to the present invention, packet-switched voice calls directed to a mobile subscriber unit that is busy in a circuit-switched call are accommodated without rejecting the voice packets. Either the information in the packet switched voice call is forwarded to a destination other than the mobile subscriber unit, or the mobile subscriber unit is notified that the packet-switched voice call is waiting.